The invention is concerned with the field of "melt applicators" or "melt dispensers". While most of the prior art (referenced herein) tends to focus upon the use of these applicators for the melting of adhesives, it is not my intention to limit the scope of this invention to that purpose alone as it is applicable to the dispensing of any thermoplastic material. Broadly, the invention relates to new and improved melting chambers for such dispensers.
Any "melt applicator", "melt dispenser", "glue gun", "adhesive dispenser", etc., can be functionally divided into at least three groupings of components:
(1) A melt assembly or melting assembly consisting of a thermally conductive housing (referred to herein as a "melt housing") having an internal melting chamber; a means for heating; a means for controlling or regulating heating temperature (in some prior art this may be integral to the heating means); necessary wires or wiring to connect the electrical components to one another and to supply electrical energy for operation; a conduit means which allows for the introduction of the thermoplastic material into the melt housing (referred to as an "inlet tube", "guide tube", "feed tube" or "feeding tube"); a means for attaching the inlet tube; an exit or outlet means having features to attach or affix a nozzle or valve or similar device to limit, direct or control the flow of the thermoplastic materials. For present purposes, this grouping of parts is referred to as the "melt assembly" or "melting assembly". PA1 (2) A feed means for advancing the thermoplastic material(s) into the above melting assembly. In its simplest form it could be the thumb or other finger of the operator applying force directly to the material itself. More commonly it involves some mechanism which, when external force is applied, grips, grabs or engages the material to be melted and then advances it forward into the melt assembly. This force may be from manual actuation or hand pressure; mechanical, hydraulic or pneumatic pressure; electrical or motor-drive means; or any combination or other method thereof. PA1 (3) A means for locating, retaining and protecting the above elements (and the operator) and also including one or more of the following: handle or handles, outer casing(s), or housing; electrical power supply cables, wires, and/or connections; pneumatic or hydraulic supply lines and/or connections; spacers; insulators; fasteners; vents or venting, and the like. PA1 (1) It describes a melt chamber which is "substantially W or V-shaped in cross-section"; though it fails to specifically describe or place numerical values or numerical/dimensional relationships in its description. What might be considered as fin elements in this patent are only referred to as "undulations" or as an "undulatory perimeter". The undulations are not pronounced and, not "bladelike" enough to be effective at penetrating and melting the thermoplastic material. PA1 (2) It describes how a "thermostat unit controls the heater to maintain the temperature of material in the melting chamber at a desired level", but fails to be more specific as to the type of thermostat, type of heater (other than as generally described as an "electrical cartridge heater"), place any numerical values as to their performance ranges, temperature ranges, etc. The only temperature value shown in the complete specification is 400.degree. F. PA1 (1) Electronic circuitry is utilized so that a given selected temperature setpoint "is automatically raised a predetermined amount when the glue is flowing in order to compensate for the drop in temperature caused by the loss of heat to the glue and atmosphere". Reference is made to the effect that "the operator can set a desired temperature to which the glue is heated", but no numerical values are given as to temperature values. The patent appears to indicate a range in excess of 340.degree. F. PA1 (2) A useful numerical value of 60.degree. F. is shown as the value of temperature differential between the melt chamber and the glue when the latter is flowing through the melt chamber without the electronic compensating circuit. PA1 (3) The use of standard cartridge heaters is indicated. Great Britain patent specification No. 1,562,926, published Mar. 19, 1980, entitled "IMPROVEMENTS IN OR RELATING TO APPARATUS FOR MELTING AND DISPENSING THERMOPLASTICS MATERIAL AND METHODS OF MAKING SUCH APPARATUS" is included because the apparatus in the patent uses what is described as an "electric heater" and "a thermostat". PA1 (1) The present invention utilizes fewer blades in a far simpler configuration and the blades used in this invention do not connect with one another inside the melting chamber but are located substantially parallel to, and in-between one another. This allows for less complex tooling and potentially more reliable manufacturability. PA1 (2) The lengths, angles, geometry, or distance from either of the ports of the individual blades themselves are deliberately different so that not more that two blades will have the same physical geometry, or if they do, no more than two blades will be equidistant from the inlet port. This longitudinal "staggering" of the blades is most critical because it allows for the material passing through the melting chamber to be sequentially and gradually "bifurcated" or "trifurcated" into ever smaller or thinner streams or substreams; this improvement lessens the "stalling effect" or "hesitation" experienced by operators during the dispensing of thermoplastic materials. This effect is the result of the depletion of a surplus reservoir of molten material which forms when a melting assembly is heated but not used for dispensing. Once dispensing begins or resumes and this reservoir depletes, there can be a subsequent inability of the heating and temperature control to "keep up with" new and relatively colder material as it is introduced and advanced through the melting chamber. This is frequently misinterpreted by users or operators as a malfunction, performance shortcoming or failure and has been the focus of other prior art, patents, etc. PA1 (3) There is no specific description in U.S. Pat. No. 4,637,745 regarding the importance of having at least one such blade to bisect, intersect, and extend through and beyond the centerline axis of the melting chamber. This feature alone ensures that the relatively cool center of the material passing through the melt chamber gets more properly heated and homogenized with the relatively hotter material around it. PA1 (4) The present invention's method(s) of heating and temperature control are wholly different and improved, and offer improved performance at user adjustable temperatures. PA1 (5) There is no specific description as to any preferred height of any blade in U.S. Pat. No. 4,637,745.
This invention is concerned primarily with a unique and synergistic grouping of certain parts, materials and/or features which are located within the first grouping of elements or the "melting assembly" as described above, and which offer distinct and specific advantages over the prior art.
U.S. Pat. No. 4,637,745 to Speisebecher et al., dated Jan. 20, 1987, entitled "MELT DISPENSERS" is of interest for background, primarily because of its discussion and description of "fins" and/or "fin elements" as used in the device's melt chamber. The fin elements and "sub-elements" are numerous and complex.
Great Britain Patent Specification No. 1,402,648, published Aug. 13, 1975, entitled "IMPROVEMENTS IN OR RELATING TO APPARATUS FOR DISPENSING MOLTEN THERMOPLASTIC COMPOSITIONS" is of interest in several areas:
U.S. Pat. No. 4,059,204 to Duncan et al., issued Nov. 22, 1977, entitled "SYSTEM FOR DISPENSING AND CONTROLLING THE TEMPERATURE OF HOT MELT ADHESIVE" is of interest in several areas.
European patent application No. 90400216.9, publication No. 0 380 420 A2, applicant/inventor Peter S. Melendy, entitled GLUE STICK AND APPLICATOR", date of filing Jan. 24, 1990 describes a glue stick, specifically having an oval cross-sectional shape. In addition, it includes a glue applicator for using said glue sticks. The application suggests that only the inlet portion of the heating (melting) chamber needs to substantially resemble the glue stick, and that it can "taper from said acircular inlet to a portion having a circular transverse cross-section". The present invention uses a similar design concept by allowing for the inlet port to be capable of accepting alternate cross-sectional perimeters/shapes.
U.S. Pat. No. 4,774,123 to Michael M. Dziki, issued Sep. 27, 1988, entitled "THERMOPLASTIC BLOCK SHAPE AND MANUFACTURING METHOD" demonstrates alternative embodiments of thermoplastic materials having different and/or alternating cross-sectional shapes.
U.S. Pat. No. 5,041,482 to Robert L. Ornsteen et al., issued Aug. 20, 1991, entitled "COOL MELT GLUE" is informative regarding the preferred temperature ranges of prior art thermoplastic materials and application equipment.
U.S. Pat. No. 4,523,705 to Richard W. Belanger et al., issued Jun. 18, 1985, entitled "MECHANISM FOR GLUE GUN" deals with the issue of "excessive force" as it applies to the use and operation of glue guns. The excessive force is usually applied when the user of the gun attempts to force cold glue through a heating chamber which has not been given adequate time to reach the optimum temperature for operation of the gun. The solution offered by this patent suggests the use of spring features or mechanical fuse features to compensate for the excessive force applied.
The solution offered by the present invention is different. By providing a combination of improved heating and temperature control, in conjunction with an improved design to the melting chamber, the time to reach optimum temperature for operation of the gun or what is referred to herein as "recovery time" is significantly reduced. The issue of "excessive force" is thereby obviated.
U.S. Pat. No. 2,389,686 to F. Reingruber et al., issued Nov. 27, 1945, entitled "THERMOSTAT" relates to a surface mounted expansion/conduction type of thermostat as is preferred for this invention.